1. Field of the Invention
The present invention relates to electron tubes, such as fluorescent luminous tubes for optical print heads, fluorescent display tubes, flat cathode-ray tubes, and vacuum tubes, each in which cathode filaments, linear grids, linear getters, and linear dampers or linear spacers for them are provided. Particularly, the present invention relates to vibration absorbing means that can dampen linear members such as cathode filaments.
2. Description of the Prior Art
FIG. 9 is a schematic view illustrating a fluorescent luminous tube for an optical print head, which is an example of electron tubes provided with conventional filament vibration absorbing means (for example, refer to Japanese Patent Laid-open Publication No. Tokkai-hei 03-257743).
FIG. 9(a) is a plan cross-sectional view illustrating a fluorescent luminous tube for an optical print head. FIG. 9(b) is a cross-sectional view illustrating a fluorescent luminous tube for an optical print head, taken along line X1-X1 shown in FIG. 9(a). FIGS. 9(c) and 9(d) are enlarged views, each illustrating a filament vibration absorbing means. FIG. 9(c) is a cross-sectional view illustrating a filament vibration absorbing means, taken along line X2-X2 in FIG. 9(b). FIG. 9(d) is a side view illustrating a filament vibration absorbing means, taken from the direction X3 in FIG. 9(c).
In the fluorescent luminous tube, the envelope is formed of a front substrate 111, a back surface 112, and side members (side plates) 121 to 124. A plurality of anode electrodes A, on which a fluorescent substance is coated, are formed in a staggered state on the front substrate 111. Anchors 131 and 132 sustaining a filament F are mounted on the substrate 111. A vibration absorber 14 for absorbing vibration of the filament F is disposed adjacent to the anchor 131. A stopper 15 is mounted to regulate the vibration absorber 14 moving in the longitudinal direction of the filament F.
The vibration absorber 14 is made of a metal strip. One end of the strip is bent to surround the filament F and is welded at the welding spot 141 and the other end thereof is bent and is in contact with the front substrate 111. Referring FIG. 9(b), when the filament F, for example, vibrates vertically, the vibration absorber 14 swings vertically to damp the vibration of the filament F.
When assembling a fluorescent luminous tube, the conventional vibration absorber has to be fabricated by bending the metal strip so as to surround the filament and then welding it. However, since the filament is very thin (for example, about 30 μm), it is difficult to bend and weld the metal strip and cinder dusts are sputtered out from the metal strip during welding. Moreover, an electron emissive material (such as carbonate), which is coated over the surface of a filament, may be damaged due to high welding temperatures during welding. Moreover, part of the electron emissive material may be peeled off as flakes. For that reason, it is required to remove those wastes.
The conventional vibration absorber, made of a metal, has a large thermal conductivity, so that the heat of the filament tends to be dissipated. This leads to largely cooling the end of a filament by the vibration absorber. Finally, this becomes an obstacle to miniaturization of electron tubes, such as fluorescent luminous displays.